Project Summary/Abstract Lung cancer is the leading cause of cancer-related mortality in the United States and worldwide. Recent improvements in lung cancer treatment have come from the identification of distinct patient subgroups with targetable molecular drivers. The current paradigm is typified by the treatment of EGFR mutant non-small cell lung cancer (NSCLC) with the targeted tyrosine kinase inhibitor (TKI), erlotinib. An emerging subgroup are those 8-14% of NSCLC patients with targetable alterations in the hepatocyte growth factor (HGF)/c-Met (MET) pathway. Lung cancer patients with either MET amplification or certain MET mutations, respond to MET targeted therapies, such as the TKI crizotinib. However, patients with MET-driven NSCLC often demonstrate de-novo resistance or inevitably develop acquired therapeutic resistance to crizotinib. The molecular factors influencing resistance to targeted TKIs in EGFR mutant NSCLC are well characterized and the pro-apoptotic protein, BIM, has been shown to be required for response and decreased levels of BIM have been shown to lead to therapeutic resistance. However, the role of BIM in response and resistance to crizotinib in MET-driven NSCLC remains poorly elucidated. Given the inevitability of resistance to crizotinib, there is significant need for studies identifying the molecular factors and mechanisms that contribute to resistance. Interestingly, we have previously shown that TWIST1, an epithelial-mesenchymal transition transcription factor that is commonly overexpressed in NSCLC and associated with poor survival, is required for MET-driven NSCLC tumorigenesis. We have also shown that TWIST1 can regulate BIM expression and TWIST1 overexpression can lead to crizotinib resistance in a MET amplified NSCLC cell line. Therefore, we hypothesize that direct suppression of BIM transcription by TWIST1 promotes crizotinib resistance in MET amplified/mutant NSCLC. To elucidate the mechanisms by which TWIST1 regulates BIM expression and leads to crizotinib resistance, we propose the following aims: Aim 1: Determine the mechanisms of TWIST1 suppression of BIM expression. We will investigate whether TWIST1 is directly suppressing BIM transcription. We will also explore if TWIST1 is indirectly regulating BIM expression by influencing the AKT2/FOXO3a signaling axis and/or influencing ERK signaling. Aim 2: Determine the role of TWIST1 in mediating crizotinib resistance in MET-driven NSCLC. Using both in vitro and in vivo models of MET- driven lung cancer, we will determine if TWIST1 overexpression can lead to crizotinib resistance, if TWIST1 suppression of BIM expression is the dominant mechanism by which TWIST1 promotes crizotinib resistance, and if inhibition of TWIST1 can increase crizotinib sensitivity. Overall, this study will further elucidate the biology of TWIST1 in MET-driven NSCLC and determine if BIM and TWIST1 are potential biomarkers of response and resistance to crizotinib, respectively. Additionally, these proposed studies will provide the rationale for TWIST1 inhibitors as a strategy to prevent and/or overcome therapeutic resistance in MET-driven NSCLC.